Generally, a film material, for preventing adhesion of a substance which will be causative of odor or pollution, is applied on a surface of a heat exchanger. A substance having a functional group and having high polarity tends to adhere to a metal base member which has a complex surface shape such as tubes or fins of a heat exchanger, and once it adheres thereto, further adhesion cannot be prevented easily. It is therefore necessary for the base material to have a function to degrade such the substance as soon as it adheres thereto. For example, in JP-A-8-296992 or JP-A-12-24512, a heat exchanger is imparted with deodorizing and sterilizing functions. That is, a photocatalyst (a film of titanium dioxide) is applied to an aluminum fin surface of the heat exchanger.
Although not particularly limited to a heat exchanger, there is an attempt to prevent odor generation by adding a silver salt, as a sterilizer, to a film component (polymer film), thereby sterilizing microorganisms attached thereto.
The heat exchanger proposed in the above patent gazettes however needs installment of a lamp for a photocatalyst (lamp for irradiating UV), which causes problems such as cost increase and durability of a lamp, particularly durability against vibration when it used in a vehicle air conditioner. Moreover, dusts from a blower fan adhere to a lamp, so an irradiation intensity may be lowered.
In the heat exchanger proposed in the above-described patent gazettes, since a film is formed on an aluminum surface with titanium dioxide as a photocatalyst, peeling occurs easily and durability is low. Accordingly, it difficult to maintain fundamental performances or productivity of the heat exchanger. In particular, when an inorganic substance such as titanium dioxide scatters by an air flow of a temperature controller, a dust odor may be caused.
Thus, a polymer film may be used instead of a titanium dioxide film, and addition of a sterilizer (the above-described silver salt, etc.) to the polymer film may be considered as a countermeasure against the above-described problem. However, in this case, elution of the sterilizer occurs, leading to problems in capacity and durability.
On the other hand, JP-A-9-175801 proposes a polyaniline film having an active oxygen generating function, and capable of carrying out deodorization and sterilization due to active oxygen. The polyaniline film has a high capacity of generating a superoxide capable of degrading a variety of odor materials compared with ordinarily employed sterilizers.
The film surface of a heat exchanger needs to have hydrophilic, but a polyaniline film is essentially hydrophobic. Accordingly, when a polyaniline film is directly used, wettability of water droplets adhering to the film is deteriorated. Therefore, water droplets scatter by the air flow, and it is difficult to maintain the fundamental performances of the heat exchanger. For example, scattering of water droplets leads to inconveniences such as supply of air mixed with water vapor to a user.